The present invention is directed to a fabrication technique for use in the manufacture of a semiconductor device; and, more in particular, the invention relates to a technique which is effective in a wet cleaning treatment performed in the fabrication of a semiconductor device.
In the fabrication of a semiconductor device, a wet cleaning technique proposed by the RCA company in the USA (so-called RCA cleaning) has been used generally as a method of removing contaminant materials, such as obstacles or metals which are deposited or which remain on the surface of silicon substrates.
RCA cleaning is a cleaning technique comprising, in combination, (1) a dipping treatment using a mixed solution of ammonium hydroxide (NH4OH)+hydrogen peroxide (H2O2)+water (referred to as SC-1 solution or APM solution) at 80xc2x0 C. for about 10 to 20 min, (2) a dipping treatment using a hydrofluoric acid (HF) at room temperature for several tens of seconds and (3) a dipping treatment using a mixed solution including hydrochloric acid (HC1)+hydrogen peroxide+water (referred to as SC-2 solution or HPM solution) at 80xc2x0 C. for about 10 min. Among the cleaning solutions described above, the SC-1 solution is used mainly for removing obstacles and the SC-2 solution is used mainly for removing metal contaminants. Further, hydrofluoric acid is used for removing silicon oxide films, which become unnecessary in the course of the steps of the fabrication method, or spontaneous oxide films.
Metal contamination on the surface of the silicon substrates tends to diffuse due to the subsequent heat treatment, such as by oxidation, into gate insulation films or substrates, so as to bring about degradation of the device characteristics, such as deterioration of the insulation withstand voltage for the gate insulation films, fluctuation of gate insulation film/substrate interface energy level and pn-junction destruction. Particularly, in recent years in which integrated circuits are constituted by refined devices, LSIs suffer from degradation of the device characteristics due to metals even when present in an extremely small amount, on the surface of the silicon substrates. Therefore, in view of the fabrication yield of the LSI, how to remove metal contamination effectively in the cleaning step is a predominant consideration.
The SC-2 solution (mixed solution of hydrochloric acid+hydrogen peroxide+water) used for removing metal contamination in the RCA cleaning method described above has no etching function by nature, so that it is difficult to effectively remove metal contamination, such as Cu (copper) taken into the surface of the silicon substrates. Accordingly, various improved SC-2 solutions have been proposed with an aim of enhancing the metal removing function of the SC-2 solution. The textbook of Chan and Sze (Chang and Sze, xe2x80x9cULSI Technologyxe2x80x9d, McGRAW-Hill, 1996, p 60-104) and literatures cited therein give detailed explanations of such SC-2 solutions.
Japanese Laid-open Patent Application Hei 3(1991)-208899 discloses a technique for removing metal contaminants and fine particle contaminants together in the cleaning of wafers by using an aqueous solution containing 0.1% or more of hydrochloric acid, 0.05 to 10% of hydrofluoric acid and 0.05 to 10% by weight of hydrogen peroxide heated to 60xc2x0 C. to 80xc2x0 C.
Japanese Laid-open Patent Application Hei 8(1996)-031781 discloses a technique for removing metal contamination on the wafer surface and contaminants in surface oxide films by using an aqueous solution containing 0.17% of hydrochloric acid, 0.25% of hydrofluoric acid and 0.1 to 0.2% of hydrogen peroxide.
Japanese Laid-open Patent Application Hei 8-264499 discloses a technique for removing metals on a wafer surface, particularly, Cu (copper), by using an aqueous solution at 60xc2x0 C. or lower, containing 0.5-3 mol/L of hydrochloric acid, 0.3 to 2.5 mol/L of 0.25% hydrogen peroxide and 0.01 to 0.3% by weight of hydrofluoric acid.
Japanese Laid-open Patent Application Hei 3(1991)-228327 discloses a technique for removing heavy metal contamination by dipping wafers in an aqueous solution at a normal temperature, the solution containing 3% of hydrochloric acid, 0.4% of hydrofluoric acid and 5% of hydrogen peroxide.
Japanese Laid-open Patent Application Hei 5(1993)-166777 discloses a technique for removing cross contamination with a smaller number of steps by using an aqueous solution containing 0.7% of hydrochloric acid, 0.5% of hydrofluoric acid and 0.15% of hydrogen peroxide.
The present inventors have made a study of the problems caused in a case of applying a SC-2 solution to cleaning steps for an LSI fabricated according to the design rule of 0.18 xcexcn or less.
As has been described above, for removing metal contamination on the surface of silicon substrates by using an SC-2 solution (hydrochloric acid+hydrogen peroxide+water), since the SC-2 solution has to be kept at a high temperature of about 80xc2x0 C., there exists a problem in that the cleaning apparatus consumes a great amount of electric power. Further, there is also a problem in that the composition of the cleaning solution fluctuates greatly because of high temperature treatment, leading to an increase in the frequency of exchanging the chemical solution. Furthermore, there is also a problem in that the space required for installing the cleaning apparatus is increased since a heating facility is necessary.
In the recent situation concerning wafer-by-wafer treatment, along with the increasing size of wafers, a short time treatment has been required for the cleaning step from the view point of improving the throughput. However, the SC-2 solution requiring a high temperature and long time treatment hinders wafer-by-wafer treatment in the cleaning steps.
The effect of metal contamination has become conspicuous along with refinement of the devices, and an extremely low metal contamination level is required for deep sub-micron devices. However, since the SC-2 solution used for removing the metal contamination has no etching function, it can not effectively remove metal contamination taken into the substrate surface or the gate insulation film surface. On the other hand, various kinds of improved SC-2 solutions in which hydrofluoric acids are added to the SC-2 solution exhibit an improved etching function for a silicon substrate or a silicon oxide film by scraping the silicon substrate or the silicon oxide film to simultaneously remove metals deposited on the surfaces thereof; however, they tend to scrape the silicon substrate or the silicon oxide film excessively so as to possibly deteriorate the device characteristics.
Particularly, as a countermeasure for compensating gate delay along with refinement of gate electrodes in a deep sub-micron MISFET, metal material such as W (tungsten) is introduced into the gate electrode materials. Therefore, while there has been a demand for a cleaning technique capable of efficiently removing metal contamination after the fabrication of the gate electrode, when cleaning at a high temperature and for a long time using a SC-2 solution containing hydrogen peroxide for ionizing W, the W film constituting the gate electrode is scraped and eliminated. Further, when an improved SC-2 solution containing hydrofluoric acid as described above is used, since hydrofluoric acid etches the gate oxide film at the lower portion of the gate electrode side wall, this may possibly deteriorate the characteristics of the device.
An object of the invention is to provide a technique which is capable of reducing the electric power consumption in a cleaning apparatus.
A further object of this invention is to provide a technique which is capable of improving the cleaning performance in the fabrication of a semiconductor device.
A still further object of this invention is to provide a technique which is capable of reducing the frequency at which the chemical solution needs to be replaced during cleaning.
Another object of this invention is to provide a technique which is capable of decreasing the space needed for installing a cleaning apparatus in the fabrication of a semiconductor device.
Still another object of this invention is to provide a technique which is capable of reducing the cost of the cleaning apparatus.
Yet another object of this invention is to provide a technique which is capable of preventing elimination of a gate electrode during cleaning after patterning a polymetal gate electrode.
A further object of this invention is to provide a technique which is capable of efficiently removing metal contamination with no unnecessary etching or a silicon substrate or a silicon oxide film.
The foregoing and other objects, as well as novel features of this invention, will become apparent from the descriptions provided in the present specification and from the accompanying drawings.
Outlines of typical aspects and features of the invention disclosed in the present application will be briefly explained below.
This invention uses, as a cleaning solution for removing metal contamination on the surface of a semiconductor wafer, an aqueous solution containing 0.1 to 15% by weight of hydrochloric acid, 0.01 to 0.3% by weight of hydrofluoric acid and 0.1 to 15% by weight of hydrogen peroxide. The concentration of the hydrochloric acid, hydrofluoric acid and hydrogen peroxide is, preferably, 0.3 to 5% by weight, 0.02 to 0.2% by weight and 0.3 to 5% by weight, respectively, and, more preferably, 0.5 to 3% by weight, 0.03 to 0.1% by weight and 0.5 to 3% by weight, respectively.
Further, the ratio of hydrochloric acid to hydrofluoric acid contained in the aqueous solution is hydrochloric acid: hydrofluoric acid=5 to 1500:1 (weight ratio), more preferably, hydrochloric acid: hydrofluoric acid=5 to 1000 1 (weight ratio) and, further preferably, hydrochloric acid hydrofluoric acid=10 to 30:1 (weight ratio).
Further, outlines of other features of the invention as described in the present application are paraphrased in the following.
1. A method of fabricating a semiconductor device includes the steps of:
(a) forming a first film pattern containing a film of a refractory metal base (usually tungsten at high purity, alloy with other metal such as a refractory metal, and those with addition of other additives) on the surface of a silicon base usually impurity doped silicon single crystal region, and other such as silicon germanium alloy, silicon germanium carbon alloy regions) on a first main surface of a wafer,
(b) acting a first alkaline cleaning solution on the first main surface of the wafer formed with the first film pattern,
(c) acting a second acidic cleaning solution containing hydrofluoric acid, hydrochloric acid, hydrogen peroxide and water on the first main surface of the wafer formed with the first film pattern and
(d) applying a high temperature heat treatment at a temperature exceeding 600xc2x0 C., after completing both of the step (b) and step (c) to the wafer without cleaning by a third cleaning solution containing hydrofluoric acid different in the composition from the second cleaning solution.
2. In the fabrication method for a semiconductor device according to paragraph (1) above, the film of the refractory metal base is a film including tungsten or molybdenum as a main constituent ingredient.
3. In the fabrication method for a semiconductor device according to paragraph (2) above, the first cleaning solution contains ammonium hydroxide, hydrogen peroxide and water.